The present invention relates to an automated method and system for image processing of images, and more specifically but not exclusively, to an automated method and system for automatic orientation of a radiographic image.
Radiographic images of anatomical regions are a routine and valuable diagnostic and research tool.
Such images are typically produced by placing an object, such as a portion of the human body, on a plate having a surface composed of excitable phosphors (a film). Next, the object and the film are exposed X-rays. As the radiation energy strikes the surface of the film, a portion of the energy is stored by the phosphor-containing film.
Upon subsequent stimulation by visible light or other stimuli, the film gives off light in direct proportion to the amount of energy stored therein. Areas of the film receiving unattenuated radiation absorb the most energy and thus produce the most light when subsequently stimulated. Areas in which lesser amounts of radiation energy are absorbed, due to the presence of the object (e.g., body region), produce a proportionately lesser amount light when subsequently stimulated.
The image may be displayed for viewing in one of several ways. For example, the stored energy of the film may be photoelectrically detected and converted into a signal. The signal is then further processed or used to reproduce the image on a photographic film, a CRT (Cathode Ray Tube) device, or similar device. With X-rays the film is usually chemically developed.
The positional orientation of the anatomical region of interest with respect to the film is of perhaps obvious critical importance to the image interpreter (e.g., radiologist), as well as for further processing of the image.
Most radiologists interpret films from light boxes. When the films are brought to the light boxes and placed by radiologists, technicians, secretaries, or other personnel, the films are expected to have a correct orientation to facilitate proper reading and interpretation.
Correct orientation takes on increased importance where radiologists compare the newly acquired film with one or more previous films of the anatomical region of interest.
Proper positional orientation of an image is also necessary for automated image enhancing and reading systems, which often assume an arbitrary positional orientation for any given image signal.
For example, where an image is viewed on a CRT or similar device the positional orientation is assumed to be parallel with the longitudinal direction of the rectangular phosphor surface on which the image was created (i.e., the neck portion of the image is aligned with the “top” of the film).
Accordingly, feeding an image signal oriented in any position other than parallel with the longitudinal direction of the phosphor surface produces errors in the display. Furthermore, feeding an image signal oriented in any position other than parallel with the longitudinal direction of the phosphor surface also prevents accurate further enhancement and/or processing of the image.
Due to the importance of the orientation of the image, many prior art attempts at detecting positional orientation of a radiographic image are known.
For example, one prior art method compares the sum of intensity values of the image signal of a horizontal strip of the subject film with the sum of the intensity values of the image signal of a vertical strip of the subject film.
The strips are taken from the subject film without differentiating the source of the intensity values within the strip (i.e., there is no way to tell if the intensity values are from the body region of interest, the background or the foreground).
Accordingly, if a portion of the foreground (which has very low intensity values) or background (which has very high intensity values) of the film is included in the strip, the calculations of distribution are skewed in one or both directions. In such instances, the ultimate determination of orientation lacks consistency and is thus unreliable.
Another prior art method utilizes a comparison of the characteristic values (sum of the intensity values and the average intensity value) for a horizontal strip of the film and for a vertical strip of the film. The method aims at ensuring that the strips pass through the central portion of the image. However, the method lacks any differentiation of the source of the image values used in the calculations. Thus, it is also impossible with this prior art method to determine whether, and by how much, the results are skewed by the inclusion of a portion of the background and/or foreground of the film. An additional problem associated with this prior art method is that the method assumes perfect alignment of the body region of interest on the film to ensure that the strips are taken through the central portion of the image. This assumption ignores the reality of actual image production.
Another prior art method is taught by U.S. Pat. No. 4,870,694, to Takeo, filed on Mar. 24, 1988, entitled “Method of determining orientation of image”. Takeo teaches determining orientation of an image of a human body by comparing distribution of the image signal level in the vertical direction of the image with the distribution of the image signal level in the horizontal direction. However, the Takeo method is computationally intensive.
U.S. Pat. No. 5,506,918, to Ishitani, filed on Dec. 23, 1992, entitled “Document skew detection/control system for printed document images containing a mixture of pure text lines and non-text portions”, teaches a document skew detection apparatus.
The apparatus taught by Ishanti includes an image extraction section for extracting from the document image a local image region. The local image region contains pure text lines occupying an almost entire area thereof.
The Ishanti apparatus further includes a skew detection section, for detecting a direction of orientation of the text lines of the local region. The skew detection section also determines an angular difference between a detected direction and a reference direction as a skew angle of the printed document.
However, the Ishanti apparatus is suitable only for images which contain text.
There is thus a widely recognized need for, and it would be highly advantageous to have, a system devoid of the above limitations.